DESCRIPTION: (Applicant's abstract): Motor neurons die selectively in amyotrophic lateral sclerosis (ALS) and during embryonic development. At present, the precise mechanisms responsible for motor neuron death are not known. The proposed experiments will determine whether different motor neuron populations in human and developing rats differentially express molecular subtypes of non-NMDA GluR. The first aim will test the hypotheses that the expression and localization of specific molecular subtypes of non-NMDA GluR are different in motor neuron populations in human CNS and that the GluR phenotypes of surviving upper and lower motor neurons are changed selectively in spinal cord and selective brain regions in individuals with ALS. The second aim proposes that subunit switches in the expression of specific GluR in motor neurons occur prior to or during developmental cell death in the rat.